After Liverpool took the lead at the London Stadium when James Milner was clearly offside in the buildup, Klopp felt Friend was aware of the error and then favoured West Ham following the half-time break.

"[We] scored a goal which I heard after the game was offside, which explains a little bit the second half," Klopp said. "I think the ref knew at half-time, I only knew after the game.

"He knew it, for sure, at half-time and then you saw there was a lot of strange situations -- not decisive, just rhythm-breakers. That obviously didn't help us.

"In the second half there were so many situations -- 50-50s, 60-40s or whatever -- and a free-kick for the other team. As a human being, if I would have known that I had made a big mistake in the first half [then] I don't want to open the gap up a bit more.

"The refs are obviously human beings and I understand that. In the game I did not understand it because I had no clue that our goal was offside."